This invention relates to transistors and particularly to an improved SOI body contract structure and process for creating such a structure in a manufacturing environment.
Glossary:
BC refers to a transistor of the body contacted type.
PC represents a shape that denotes the shape of poly-silicon structures.
RX represents a shape that denotes an opening in the field oxide, exposing active silicon.
Delta-W is the difference in finished manufactured dimension from the dimension drawn in the design.
Dog bone or DOG BONE means a contact shaped as shown in FIG. 11 having a shape generally like an xe2x80x9cHxe2x80x9d, dog bone or femur.
Top-to-top xe2x80x9cTxe2x80x9d refers to a shape that generally denotes two xe2x80x9cTxe2x80x9ds which are mirror images of one another having their tops aligned in a generally parallel direction as illustrated by FIG. 10. Trademarks: S/390 and IBM are registered trademarks of International Business Machines Corporation, Armonk, New York, U.S.A. and Lotus is a registered trademark of its subsidiary Lotus Development Corporation, an independent subsidiary of International Business Machines Corporation, Armonk, N.Y. Other names may be registered trademarks or product names of International Business Machines Corporation or other companies.
Background:
A standard, non body contacted transistor will be described as is usually drawn as shown in FIG. 8 below. The areas labeled xe2x80x9cSxe2x80x9d and xe2x80x9cDxe2x80x9d represent the source and drain of the transistor. The gate is labeled with the word xe2x80x9cGate.xe2x80x9d The effective width of this transistor is determined only by the width of the RX opening in the oxide, which is the outer rectangle in this illustration. Any Delta-W term is due to any bias on the oxide opening. The tolerances that have to be included when computing the width are the RX image size and any tolerance on Delta-W. By special use of an existing process, the standard transistor structure can be improved and is useful in making complex circuits such as those used by IBM""s S/390 processors. The problem with prior and existing SOI xe2x80x9cBCxe2x80x9d type body contact structures is that the cause the effective transistor width to vary depending upon the overlay tolerance between the PC and RX levels.
The invention illustrated in top view in FIG. 7, and provides a transistor in which the top part of the transistor can be and preferably is the same as existing structures, but the bottom part is the mirror image of the top part, and in the bottom part, the effect of PC to RX overlay is reversed, an xe2x80x9cUPxe2x80x9d misalignment will make the device width larger, while a xe2x80x9cDownxe2x80x9d misalignment will make the device width smaller. This removes the overlay tolerance from the effective transistor width.